1. Field of the Invention
This invention relates to a method and an apparatus for collecting and analyzing data, and more particularly, for collecting and analyzing data pertaining to the center of pressure beneath a standing subject's feet as an upright posture is maintained.
2. Background of the Prior Art
The task of maintaining an upright posture involves a complex sensorimotor system. Even when a young, healthy individual attempts to stand still, the center of gravity of his or her body and the center of pressure under his or her feet move relative to a global coordinate system.
A plot of the time-varying coordinates of the center of pressure beneath the feet of a standing subject is known as a stabilogram. One such stabilogram is shown in FIG. 1. By studying signatures of the center of pressure, researchers have attempted to correlate the center of pressure with the dynamics of the neuromuscular postural control system working to maintain human balance.
For example, a number of biomechanical researchers have attempted to evaluate postural sway by using a force platform to measure the anteroposterior and mediolateral displacements of the center of pressure over the plane of support. Other researchers have limited the analysis of center of pressure trajectories to summary statistics, e.g., the calculation of the length of the sway path, average radial area. In either case, the data obtained in prior static posturography have been limited by the lack of a reliable, consistently useful method for extracting repeatable, physiologically meaningful information from stabilograms. In other words, since the signature of the center of pressure will not repeat itself even when tests of the same subject are taken immediately after one another, it has been difficult to interpret the data obtained from the center of pressure signatures.
Within the neuromuscular postural control system there are known closed-loop feedback systems. The closed-loop feedback systems synthesize information from visual, vestibular, and somatosensory receptors. During any given task, the human postural control system receives information from these receptors, and depending upon the information received, corrective postural control signals are sent to the neuromuscular system. The corrective postural control signals from the visual, vestibular, and somatosensory systems are analogous to a closed-loop feedback control system. It has generally been thought that these afferent signals (visual, vestibular and somatosensory) were the exclusive regulators of the musculature during quiet standing. However, traditional clinical results have overlooked possible short term open-loop control schemes operating on the postural control system before the long term closed-loop system activates.
In the past, researchers have attempted to correlate the effect that the visual, vestibular and somatosensory systems have on postural control. One leading method of correlating the effect of these systems on postural control is known as the Romberg test. This test involves the comparison of an individual's quiet-standing postural sway under eyes-open and eyes-closed condition. Since, as with other traditional analyses of stabilograms, the Romberg test analyzes the results of the stabilogram based on, for example, maximum displacement and total distance traversed, the interpretation of the results obtained from the Romberg test has been limited by the inability to obtain repeatable, physiologically meaningful information from stabilograms. Nonetheless, according to the conclusions of the Romberg test, postural instability, as measured by center of pressure summary statistics, generally increases when a subject closes his or her eyes.
Other contemporary scientific and clinical investigations in postural control have directed their attention to analyzing the response of the human body to various external perturbations. Although this reflexive approach enables a clinician to examine the input/output characteristics of different closed-loop feedback systems, it does not consider explicitly the stabilizing roles of possible short term open-loop control schemes or the steady-state behavior of the human body during periods of undisturbed stance. However, since static posturography lacks a reliable, consistently useful approach or technique for extracting repeatable, physiologically meaningful information from stabilograms, a subject's balance is typically analyzed with dynamic posturography, i.e., applying an external force to the subject and monitoring the recovery of balance.
In addition, dynamic posturography, by its very nature, is considerably more hazardous and physically taxing than static posturography, especially in aged and physically infirm subjects. For example, it is much safer to analyze a person who is likely to lose his or her balance on a static force plate and monitor the postural control system at work than it is to apply an external force and then monitor the postural control system as he or she recovers his or her balance. Since, until now, there was no known way to harness the data provided by the stabilogram produced during quiet standing, many stabilogram analyses have been directed to dynamic posturography.